A supercharged internal combustion engine has already been disclosed in, for example, PTL 1. The aforementioned internal combustion engine includes an intercooler that cools supercharged intake air, and an EGR cooler that cools EGR gas that is introduced into an intake passage on an upstream side relative to a compressor. The EGR gas amount is controlled so that condensed water is not generated in the intercooler and the EGR cooler.
If introduction of EGR gas is performed during an initial warm-up stage after commencing startup from a cold state, condensed water is liable to be generated. Consequently, an EGR valve is normally closed during an initial warm-up stage. However, even if the EGR valve is in a closed state, exhaust gas is present in the EGR passage on an upstream side of the EGR gas flow relative to the EGR valve. Therefore, in some cases, as a result of moisture contained in exhaust gas touching against the cold EGR valve, condensation of moisture occurs on the surface of the EGR valve on the side that is exposed to the exhaust gas and condensed water is generated.
In order to suppress the occurrence of condensed water that is generated in the above described manner, it is conceivable to adopt a measure so as to heat the wall surface of the flow passage of EGR gas on an upstream side relative to the compressor. However, since the state is one in which the EGR valve that is being closed is sandwiched between low-temperature fresh air and the exhaust gas, it is difficult to directly heat the EGR valve itself and keep the EGR valve warm. Consequently, when the engine cooling water temperature rises after cold starting and a condition is established that allows the introduction of EGR gas, the state at such time is one in which condensed water is attached to the EGR valve surface on a side which the exhaust gas contacts against. Further, even at a time other than when warming up the engine, condensed water sometimes attaches to the surface of the EGR valve if the EGR valve that is in a closed state during engine operation is cooled by low-temperature intake air.
If the EGR valve is opened to introduce EGR gas without giving particular consideration to the generation of condensed water at the EGR valve as described above, condensed water that has attached to the EGR valve will flow into the intake passage. If condensed water that flowed into the intake passage is drawn into the compressor, there is a concern that droplets of the condensed water will collide against the impeller of the compressor and lead to the occurrence of an erosion phenomenon at the impeller.